1. Field of the Invention
The present invention relates to an encoder that is usable for various apparatuses such as optical apparatuses and outputs, with relative movement of a scale and a sensor, a signal showing position of a movable member provided in the apparatus.
2. Description of the Related Art
Encoders that are used to detect position and speed of a movable member are constituted by a scale and a sensor; the scale is provided with a periodic pattern and attached to, for example, a movable member, and the sensor is attached to a fixed member and reading the periodic pattern to output a signal corresponding to the position of the movable member. Such encoders perform an interpolation process by calculating a phase from plural phase periodic signals (two or three or more phase periodic signals) output from the sensor with relative movement of the scale and the sensor.
When taking in (reading) the plural phase periodic signals not simultaneously, but sequentially, reading times of the respective phase periodic signals have a difference. In a case where the scale and the sensor are relatively moved, relative positions of the scale and the sensor at the respective reading times are mutually different. In this case, the phases of the read phase periodic signals are mutually different, and therefore the interpolation process cannot provide a correct phase that should be obtained.
International publication No. WO2000/28283 discloses an encoder that performs an interpolation process after correcting a phase of one of two periodic signals read at mutually different relative positions of the scale and the sensor to a phase corresponding to the position at which the other thereof is read.
However, the encoder disclosed in International publication No. WO2000/28283 requires multiple trigonometric calculations for the correction, which increases load for signal processing and thereby may require a high-cost signal processor. Moreover, the encoder requires insertion of a process for the correction into a process for detecting the phase, which makes it difficult to use an existing signal processor without change.